Lincoln Walsh

Lincoln Walsh (November 3, 1903 – November 17, 1971) was educated at Stevens Institute of Technology, Columbia University and at Brooklyn College. Before World War II, he founded the Brook Amplifier Company. During the war, he worked with Rudy Bozak at the Dinion Coil Company in Caledonia, New York, developing high voltage power supplies for radar use. Walsh worked as a member of the War Planning Board, where he met and later married Harriet Walsh. They were residents of Millington, New Jersey for many years. They had no children.

Walsh may have been involved in the development of the Kettledrum Baffle that one associates with the first Bozak speaker systems. He redesigned the "Mark II" (Colossus computer?) power supply to prolong the unit's life. Later, he was a consultant on very large transformer designs for power distribution. He also developed a high-quality AM radio receiver and an aircraft collision avoidance system.

His interests extended to loudspeaker design. With the help of Bozak, he developed a direct-radiator design using a single speaker with an aluminum foil cone, operating out of a vertical column, and offering a wide frequency response. A Simple Quality Rating System for Loudspeakers and Audio Systems appeared in the Journal of the Audio Engineering Society for July, 1963. He went on to invent the wide-range coherent transmission-line loudspeaker, which was granted U.S. Patent 3,424,873 in 1969 (filed in 1964).

In 1971, Martin Gersten founded Ohm Acoustics. Gersten raised the capital needed to buy back the Walsh patent rights from a metal-casting company which had invested with Walsh. Walsh's new speaker design was developed and marketed by Ohm (the Ohm 'A'), after Gersten invented an edge-wound anodized aluminum voice coil, U.S. Patent 3,835,402 (1974), which was needed to make the unit viable.

Unfortunately, Walsh died before his speaker was released to the public. Current Ohm Chief Engineer, John Strohbeen further developed Walsh's concepts.

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Pioneer SX-1980

The Pioneer SX-1980 was a receiver that Pioneer Electronics Corporation introduced in 1978, to be matched with the HPM series of speakers. It is rated at a staggering 270 watts per channel into 8 ohms.However, in the September 1978 issue of Audio Magazine, Leonard Feldman did a spec test on the SX-1980 and concluded that the rating of 270 watts per channel was too conservative. He stated in his report:

"Though the new [IHF mandated] "Dynamic Headroom" measurement is specified in dB, it should be mentioned that based upon the short-term signal used to measure the 2.3 dB headroom of this amplifier, it was producing nearly 460 watts of short-term power under these test conditions!"

At an official rating of 270 watts per channel into 8 ohms with a 2.3 dB dynamic headroom, this makes the SX-1980 Pioneer's most powerful receiver, as well as being one of the most powerful receivers ever manufactured in the world, to date.Nothing had been built like it before, and nothing has been built like it since.

The SX-1980 is known for its total harmonic distortion (THD) rating of less than 0.03%, an astounding feat that has only been replicated by very few receivers at such a high power output; a feat that has not been replicated by Pioneer or any other receiver manufacturer since the late 1970s.Along with sheer power and extremely low THD, it is also known for its reliability and workmanship, as many fully functional units still exist in complete working order today. According to the owner's manual:

The adoption of a single-stage differential amplifier with low-noise dual transistors, a current mirror load and a 3-stage Darlington triple SEPP circuit provides a bumper power output of 270 watts + 270 watts (20 Hertz to 20,000 Hertz with no more than 0.03% THD) which is extremely stable. The power amplifier is configured as a DC power amplifier with the capacitors removed from the NFB circuit for a flat gain response. The large-sized toroidal transformers with their superb regulation employ 22,000uF large-capacity electrolytic capacitors (two per each channel). There are independent dual power supply circuits with separate power transformer windings to provide power for the left and right channels. The FM front end incorporates a two-stage RF circuit that employs a 5-gang tuning capacitor and three dual gate MOS FETs for high gain and low noise. This configuration excels in ridding the sound of undesirable interference. The FM IF amplifier combines five dual-element ceramic filters…for high selectivity (80dB) and low distortion… The local oscillator includes Pioneer’s very own quartz sampling locked APC (Automatic Phase Control). This output of this extremely precise quartz oscillator is divided into frequencies of 100 kHz and so reception frequencies which are a multiple of 100 kHz are locked at every 100 kHz.

The SX-1980 is 22 inches wide, 19.5 inches deep, and 8.25 inches high; weighing 78 pounds.The case, like the Pioneer HPM-100, has a fine-grain, walnut veneer finish. It has massive heatsinks on the back to dissipate the immense heat the receiver can build up. Silverpioneer.netfirms.com's review of the receiver is quoted:

"The SX-1980's beauty was more than skin-deep. As Pioneer's best receiver, the careful and logical layout of the receiver's hefty toroidal transformer and four massive capacitors were flanked by the component circuit boards, a layout that was shared by the SX-1250 and SX-1280. This receiver had 12 Field Effect Transistors (FETs), 11 Integrated Circuits (ICs), 130 transistors and 84 diodes!"

It's retail price in 1978 was $1295.00. According to S. Morgan Friedman's Inflation Calculator, it would list for an equivalent of $3638.00 today.

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NorthStar Horizon

Introduced in 1979, the NorthStar Horizon was an 8-bit computer system based on the ZiLOG Z80A microprocessor. It was produced by North Star Computers, and it could be purchased either in kit form or pre-assembled.


The computer consists of a steel chassis separated into left and right compartments with a plywood cover which sat on the top and draped over the left and right sides. The motherboard was based on the S-100 bus common in its day. Although a few logic circuits were on the motherboard, primarily for I/O functions, both the processor and the memory resided in separate daughterboards. It contains an internal discrete linear power supply, including a large transformer and power capacitors, comprising much of the bulk and weight of the system.


Capable of running CP/M and NSDOS (NorthStar's proprietary Disk Operating System), a standard NorthStar system sported one or two hard-sectored 5.25 inch floppy disk drives and a serial interface to which one could connect a terminal to interact with it.

NSDOS included NorthStar BASIC, a slightly non-standard dialect of BASIC, where some standard BASIC commands of the day had been changed, probably to avoid potential legal issues. Two examples of this were the "FILL" and "EXAM" commands, which took the place of the more traditional-for-the-day "POKE" and "PEEK" statements.

Superseded by the all-in-one NorthStar Advantage in 1983, the NorthStar Horizon found a niche in University environments where its inbuilt S-100 bus could be used to interface it to a variety of control systems.

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Cathode heater

A cathode heater is a filament used to heat the cathode in a vacuum tube or cathode ray tube. Before transistors and integrated circuits came into widespread use, electronic devices used vacuum tubes. The cathode element had to achieve the required temperature in order for these tubes to function properly. This is why older electronics often needed some time to "warm up" after being powered on; this phenomenon can be observed in the cathode ray tubes of modern televisions and computer monitors.

The simplest type of vacuum tube operates as a diode: that is, it allows current to flow in only one direction. The cathode heater is used to raise the temperature of the cathode filament, permitting thermionic emission of electrons into the evacuated tube. The other element inside the tube is called the "plate", or anode. If the anode is positively charged relative to the cathode, the emitted electrons will be attracted to it, and current will flow. This exhibits the characteristics of a diode as current flow in the reverse direction is not possible (the anode is not heated, prevention thermionic emission.) More complex vacuum tubes operated as triodes (the predecessor to the modern transistor) or other circuit elements, but all tubes required some type of cathode heater in order to trigger electron emissions.

The purpose of the cathode heater is to heat the cathode to a temperature that causes electrons to be 'boiled out' of its surface into the evacuated space in the tube, a process called thermionic emission. The temperature required for modern cathodes is around 800-1000°C (1500-1800°F)

Construction
The cathode is usually in the form of a long narrow sheet metal cylinder at the center of the tube. The heater consists of a fine wire or ribbon, made of a high resistance metal alloy like nichrome, similar to the heating element in a toaster but finer. It runs through the center of the cathode, often being coiled on tiny insulating supports or bent into hairpin-like shapes to give enough surface area to produce the required heat. The ends of the wire are electrically connected to two pins protruding from the end of the tube. When current passes through the wire it becomes red hot, and the radiated heat strikes the inside surface of the cathode, heating it. The red or orange glow seen coming from operating vacuum tubes is produced by the heater.

There is not much room in the cathode, and the cathode is often built with the heater wire touching it. The inside of the cathode is insulated by a coating of alumina (aluminum oxide). This is not a very good insulator at high temperatures, therefore tubes have a rating for maximum voltage between cathode and heater, usually only 200 - 300 V.

Heaters require a low voltage, high current source of power. The voltage required was usually 5 or 6 volts AC. In older electronic devices this was supplied by a separate 'heater winding' on the device's power supply transformer that also supplied the higher voltages required by the tubes' plates and other electrodes.

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Welding power supply

A welding power supply is a device that provides an electric current to perform welding. Welding usually requires high current (over 80 amperes) and it can need above 12,000 amps in spot welding. Low current can also be used; welding two razor blades together at 5 amps with gas tungsten arc welding is a good example. A welding power supply can be as simple as a car battery and as sophisticated as a modern machine based on silicon controlled rectifier technology with additional logic to assist in the welding process.

Classification
Welding machines are usually classified as constant current (CC) or constant voltage (CV); a constant current machine varies its output voltage to maintain a steady current while a constant voltage machine will fluctuate its output current to maintain a set voltage. Shielded metal arc welding will use a constant current source and gas metal arc welding and flux-cored arc welding typically use constant voltage sources but constant current is also possible with a voltage sensing wire feeder.

The nature of the CV machine is required by gas metal arc welding and flux-cored arc welding because the welder is not able to control the arc length manually. If a welder attempted to use a CV machine to weld with shielded metal arc welding the small fluctuations in the arc distance would cause wide fluctuations in the machine's output. With a CC machine the welder can count on a fixed number of amps reaching the material to be welded regardless of the arc distance but too much distance will cause poor welding.

Machine construction
Most welding machines are of the following designs:

Transformer
A transformer style welding machine converts the high voltage and low current electricity from the utility into a high current and low voltage, typically between 17 to 45 volts and 190 to 590 amps. This type of machine typically allows the welder to select the output current by either moving the core of the transformer in and out of the magnetic field or by allowing the welder to select from a set of taps on the transformer. These machines are typically the least expensive to purchase for hobbyist use.

Generator and alternator
Welding machines may also use generators or alternators to convert mechanical energy into electrical energy. Modern machines of this type are usually driven by an internal combustion engine but some older machines may also use an electric motor to drive the alternator or generator. In this configuration the utility power is converted first into mechanical energy then back into electrical energy to achieve the step-down effect similar to a transformer. Because the output of the generator can be direct current, these older machines can produce DC from AC without any need for rectifiers of any type.

Inverter
Since the advent of high-power semiconductors such as the IGBT, it is now possible to build a switching power supply capable of coping with the high loads of arc welding. These are known as inverter welding units. These supplies generally convert utility power to high voltage and store this energy in a capacitor bank; a microprocessor controller then switches this energy into a second transformer as needed to produce the desired welding current. The switching frequency is very high - typically 10,000 Hz or higher. The high frequency inverter-based welding machines can be more efficient and have better control than non-inverter welding machines.

The IGBTs in an inverter based machine are controlled by a microcontroller, so the electrical characteristics of the welding power can be changed by software in real time updates. Typically the controller software will implement features such as pulsing the welding current, variable ratios and current densities through a welding cycle, variable frequencies, and automatic spot-welding; all of which would be prohibitively expensive in a transformer-based machine but require only program space in software-controlled inverter machine.

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Infrastructure in London

Below is information on the utility infrastructure in the city of London, England.

Electric power supply
Several power stations were built to generate electricity in the centre of London, including the famous power stations at Bankside and Battersea (both now disused). Bankside power station has now been converted into Tate Modern, but still houses part of a large electricity transformer substation.

HVDC Kingsnorth has been a unique element of the London power grid since 1975, the first urban high voltage direct current transmission system in the world. It was subsequently converted to standard 3-phase alternating current.

Water
The Thames Water Ring Main supplies much of London with water. Sewage disposal was historically a problem, causing major pollution of the River Thamesand potable water supplies. London suffered from major outbreaks of cholera and typhus well into the mid-1800s. Indeed, the problem was so severe that Parliament was suspended on occasion due to the stench from the river. These problems were solved when Sir Joseph Bazalgette completed his system of intercepting mains to divert sewage from the Thames to outfalls east of London, where the tide would sweep the sewage out to sea.

Telecommunications
There are 188 telephone exchanges in London and all offer ADSL internet services. Most of London, and some adjacent places, are covered by the 020 area code. Some parts of outer London are covered by the 01322, 01689, 01708, 01895, 01923 and 01959 codes. There is extensive wireless LAN coverage, especially in central London such as the City of London Corporation, who are developing blanket coverage for the financial district.There is wide coverage from five mobile phone networks of which four are GSM/UMTS and one is UMTS-only.

Most analogue and digital television and radio channels are received throughout the London area from either the Crystal Palace Transmitter or Croydon Transmitter in south London. Cable television is widespread with service provided by Virgin Media, however coverage is not universal. Tiscali TV provide an expanding video on demand cable television service over ADSL to the London area. Broadband internet and telephone services are also provided by the cable television networks.

With computers and technology playing a key part in the economy, companies have created a large number of datacentres within Greater London, many of which are in the Docklands area. As a result, London now hosts key parts of the Internet, including LINX (London INternet eXchange), the largest Internet Exchange Point in the world, carrying over 310 Gb/sec of Internet traffic (as of 2008).

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Push–pull converter

A push–pull converter is a type of DC to DC converter that uses a transformer to change the voltage of a DC power supply. The transformer's ratio is arbitrary but fixed; however, in many circuit implementations the duty cycle of the switching action can be varied to effect a range of voltage ratios. The primary advantages of push–pull converters are their simplicity and ability to scale up to high power throughput, earning them a place in industrial DC power applications.

The push–pull converter is similar to the flyback converter and especially the forward converter.

Circuit operation

The term push–pull is sometimes used to generally refer to any converter with bidirectional excitation of the transformer. For example, in a full-bridge converter, the switches (connected as an H-bridge) alternate the voltage across the supply side of the transformer, causing the transformer to function as it would for AC power and produce a voltage on its output side.

However, push–pull more commonly refers to a two-switch topology with a split primary winding.

In any case, the output is then rectified and sent to the load. Capacitors are often included at the output to buffer against the inevitable switching noise.

In practice, it is necessary to allow a small interval between powering the transformer one way and powering it the other: the “switches” are usually pairs of transistors (or similar devices), and were the two transistors in the pair to switch simultaneously there would be a risk of shorting out the power supply. Hence, a small wait is needed to avoid this problem.


Transistors
N-type and p-type power transistors can be used. Power MOSFETs are often chosen for this role due to their high current switching capability and their inherently low ON resistance. The gates (base) of the power transistors are tied via a resistor to one of the supply voltages. A p-type transistor is used to pull up the n-type power transistor gate (common source) and an n-type transistor is used to pull down the p-type power transistor gate.

All power transistors can be n-type (often 3 times the gain of p-type). Then the n-type transistor, which replaced the p-type has to be driven this way: The voltage is amplified by one p-transistor and one n-transistor in common base configuration to rail-to-rail amplitude. Then the power transistor is driven in common drain configuration to amplify the current.

In high frequency applications both transistors are driven with common source. In fact they are both pushing, pulling is done by a low pass filter (coil) in general and by a center tap of the transformer in the converter application. Because the transistors push alternating this device is also called a push–pull converter.


Timing
If both transistors are open, this is a short circuit. If both transistors are closed, high voltage peaks due to back EMF appear.

If the driver for transistor is powerful and fast enough, the back EMF has no time to charge the capacity of the windings and of the body-diode of the mosfets to high voltages.

If a microcontroller is used, it could measure the peak voltage and digitally adjust the timing for the transistors, so that the peak just appears (coming from no peak, starting from cold transistors in warm-up / boot-phase).

The cycle starts with no voltage and no current. Then one transistor opens, a constant voltage is applied to the primary, current increases linearly, and a constant voltage is induced in the secondary. After some time T the transistor is closed, the parasitic capacities of the transistors and the transformer and the inductance of the transformer form an LC circuit which swings to the opposite polarity. Then the other transistor opens. For the same time T charge flows back into the storage capacitor, then changes the direction automatically, and for another time T the charge flows in the transformer. Then again the first transistor opens until the current is stopped. Then the cycle is finished, another cycle can start anytime later. The S-shaped current is needed to improve over the simpler converters and deal efficiently with remanence.

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